Multiple-input multiple-output (MIMO) communication systems offer great increases in the throughput and data rate due to the ability to support multiple parallel data streams that are transmitted on different antennas.
The performance of MIMO communication systems can be further improved by using the closed-loop MIMO technology which is based on the feedback of the channel state information (CSI) from the User Equipment (UE) to the Base Station (BS). Namely, according to CSI, downlink data can be precoded at the BS before being transmitted in order to get better Signal to Noise Ratio (SNR) at the UE side and an overall larger system capacity. Said in other words, precoding is the process of prearranging the transmit signals in MIMO communication systems in consideration of CSI in such a way that the UE can combine the MIMO signals to detect the transmitted signal more reliably.
In classic MIMO communication systems, antenna arrays usually consist of only two, four, or eight physical antennas which are considered for baseband processing. Such arrangements have the advantage of limiting signal processing complexity.
However, with the advent of technologies such as massive MIMO, signal processing complexity is significantly increased. For example, as shown in FIG. 1, Full-Dimensional multiple input multiple output (FD-MIMO) which is a practical implementation of massive MIMO in wireless communication systems, places a large number of active antenna elements in a two-dimensional grid of active antenna arrays GRID at the BS.
Although, this new arrangement allows the extension of spatial separation to the elevation domain as well as the traditional azimuth domain so as to harvest the benefits of both azimuth beamforming ϕ and elevation beamforming θ, it significantly increases the complexity of such systems due to the need to process differently a large number of data.
In fact, signal processing complexity at the BS with foregoing arrangement, particularly during the precoding process, can slow down the overall processing due to the large number of physical antennas to consider. Hence, an efficient precoding process is required.